1. Field of the Invention
The present invention relates to a vibration generator. In the vibration generator of the present invention, a coil and a magnet are arranged along a radial direction. A vibrating body is vibrated in a thrust direction by an interaction between the coil and the magnet.
2. Description of the Related Art
A portable terminal such as a cellular phone or the like includes a vibration generator arranged therein. The vibration generator generates vibration to thereby notify a user of arrival of an incoming call. Different types of vibration generators are available. As one example, there is available a vibration generator in which a vibrating body is vibrated in a thrust direction by an interaction of magnetic fields generated by a coil and a magnet. There have heretofore been proposed various kinds of vibration generators in which a vibrating body is vibrated in a thrust direction.
Japanese Patent Application Publication No. 2003-93968 discloses a vibration generator in which a coil and a magnet are arranged side by side along a radial direction. The vibration generator includes a pair of brackets for holding a fixed shaft in an outer end portion of a frame made of a magnetic material. The vibration generator includes a coil wound only in one direction and arranged on an inner circumferential surface of the frame. The vibration generator includes a permanent magnet arranged in a spaced-apart relationship with the coil to magnetically interact with the coil and a vibrating body formed of a bearing. The vibrating body is arranged between the brackets and is held on the fixed shaft through a spring so that the vibrating body can move in the axial direction.
Japanese Patent Application Publication No. 2003-154314 discloses a vibration generator in which a coil and a magnet are arranged side by side along a radial direction. The vibration generator includes an outer yoke portion having a magnet. The vibration generator further includes an inner yoke portion having a coil portion arranged in an opposing relationship with the outer yoke portion to generate vibration-purpose magnetic fields. The vibration generator further includes a leaf spring for interconnecting the inner yoke portion and the outer yoke portion. The leaf spring is assembled at a balance position of the outer yoke portion in an extended state.
However, the vibration generator disclosed in Japanese Patent Application Publication No. 2003-93968 suffers from reduced vibration efficiency because the vibrating body is vibrated with the Lorentz force by directly applying magnetism to the coil. The vibrating body is supported by coil springs arranged at the opposite sides thereof. With this structure, the percentage of the coil springs in the vibration generator becomes larger, making it impossible to reduce the size of the vibration generator.
The magnetic circuit of the vibration generator disclosed in Japanese Patent Application Publication No. 2003-154314 is formed into an outer magnet structure in which the magnet is arranged radially outward of the coil. In this outer magnet structure, the percentage of the inner yoke portion in the internal space of the vibration generator grows larger. Moreover, the volume of the coil cannot be increased in the outer magnet structure. Thus, the vibrating body is caused to vibrate at desired acceleration and amplitude through the use of a high-performance magnet. For that reason, the vibration generator of outer magnet structure becomes less cost-effective.